Systems for generating images of relief objects are known. Relief objects are objects having a surface with features typically formed by ridges and valleys. A common relief object imaged by known technology is a fingerprint. These known systems include a platen to which a relief object is pressed to expose the ridges and valleys of the relief object to imaging equipment. The platen is illuminated by a light source. In many relief object imaging systems, the light from the light source is passed through a collimator before it illuminates the platen. The light is typically coupled through a right-angle prism to the platen at or near an angle corresponding to Total Internal Reflection (TIR). TIR refers to the frustration or absorption of light at the ridges of the relief object and its reflection back through the platen at the valleys of the relief object. Thus, light from the light source is modulated by the structural features of the relief object pressed against the platen and this modulated light is transmitted through the platen to an optical system. The optical system is usually comprised of lenses and other optical treating components. The optically treated, modulated light then impinges on a sensor array which converts the optical energy into electrical energy. The intensity at each element of the sensor array is typically converted to a digital value and the values for the array elements may then be processed by a computer for classification or verification of the relief object.
These known relief object imaging systems have a number of disadvantages. For one, each requires a light generating source which must be located at a distance from the platen so that a substantial portion of the platen surface is illuminated by the light source. Additionally, the optically treating elements are typically placed at a distance and angle from the platen to receive the reflected light from the platen. To optimize the benefits of the optical element processing, the optical treating elements must be located at distances from the platen where light rays converge or other known optical physical phenomenon occur. Thus, the geometry of known relief object imaging systems impose size constraints which limit the applications for known relief object imaging systems.
Another disadvantage of known imaging systems are distortions of the reflected image. For example, the platen and sensor array in a typical relief object imaging system are tilted to maintain good focus while also maintaining platen illumination near the TIR angle. This tilting causes two types of distortions known as a keystone distortion and cosine distortion. Frequently, these distortions are reduced by interposing optical elements between the sensor array and the platen. However, the interposing of additional optical treating elements exacerbates the geometric constraints for the system and further impacts the applications in which the system may be used.
Known relief object image generating systems are also sensitive to ambient light entering the platen from the surface on which the relief object is placed. Additionally, the presence of an excessive amount of moisture or oil on the relief object alters the modulation of the light by the relief object and may further degrade the image of the relief object in such systems. Likewise, an exaggerated absence of moisture and other fluids in a relief object, such as a fingerprint, may also alter the light modulation produced by the relief object and degrade the image of the relief object. Also, systems which are engineered to address image degradation caused by excessive moisture may not adequately correct degradations caused by excessively dry relief objects and vice versa.
What is needed is a relief object imaging system that reduces the geometrical constraints on the size of a relief object image generator.
What is needed is a relief object imaging system that reduces distortions in an image of the relief object.
What is needed is a relief object image generating system that reduces degradation caused by excessive moisture without increasing the likelihood of degradation caused by exaggerated absence of moisture.